Manholes are used to provide street-level access to sewer lines and other underground structures. Most often, the top portion of the manhole has the form of a cylindrical frame with a lid. The lower portion of the frame, which is not generally seen after installation, often resembles a hat with a brim that rests on a concrete cone leading to a sewer. The upper portion of the frame holds a lid. The elevation of the manhole frame and lid may be raised to the level of the surrounding surface grade by placing one or more concrete adjusting rings between the bottom of the frame and the cone. A manhole structure is thus created by stacking a number of components on top of each other. After the manhole structure is installed, the space around it is filled in so that only the lid at the top portion of the manhole frame is conveniently accessible at street-level.
Manholes created by such stacking of components are vulnerable to leaks. Water and other contaminants may enter the manhole through gaps between the stacked components after installation. Once the manhole structure has been installed and the earth around it filled in, gaps below the ground level become difficult to reach. It is thus desirable to seal the manhole structure during installation to prevent further leaks at the interfaces between the stacked components.
Various methods and devices are known for sealing the external surfaces of manhole structures. One method employs an elastomeric band positioned around the top portion of the cone and extending over the adjusting rings to the base of the manhole frame. Because the cone and the adjusting rings have generally the same outer perimeter, a single sealing band may be used to provide a seal for the gaps between these components. Although such a method provides an adequate seal for the portions of the manhole structure with a periphery corresponding to the band's periphery, i.e., lower portion of the manhole structure from the cone to the bottom of the frame, they do not adequately seal the upper portion of the frame, which has a periphery that is generally narrower than the periphery of the manhole frame's base.
Manhole structures, however, often have structural gaps in the region between the two peripheries where conventional sealing bands do not reach. For example, some manhole-frame designs have holes in the horizontal portion of the frame base that are used to retain bolts or anchors for securing the frame to the stacked components below it. Another example is the “floating” casting. A floating casting is a two-piece manhole frame with a narrower upper frame resting on a wider base flange. For such manhole frames, and for other manhole frame designs with similar leakage points, existing methods are inadequate to provide a complete seal. It is thus desirable to extend the seal from the larger outer periphery generally shared by the cone and adjusting rings to the narrower periphery of the upper frame and lid.
What is needed in the industry is a device and method for better sealing a manhole structure that can seal both the larger lower external periphery of a manhole structure and any potential leaks that may originate between the lower periphery of the manhole structure and the narrower periphery of the upper portion of the manhole frame and lid.